Incorrect Wire?

Here are a couple of pic’s from todays inspection.
There is a 40 amp double pole breaker, third on right, for the AC, that is wired using 12/2 romex? The wire for that size of breaker is to small correct? But the amps on the ac says, 23.6amp.

The second pic shows oxidation on the lead feeding the panel is this an issue that should be called out?


double pole.JPG

AC loads do not use the same wire sizes as regular branch circuits. The breakers are sized for the starting current. The wire is sized for the run current. To verify proper wire sizes you need to look at the nameplate to check the minimum circuit size.

The minimum is 23.6 amps

Hi Gary,

I can’t comment on the wire guage (but that ain’t a 12/2) it many be a 12awg, but the real issue is that the compressor is I think an upgrade from the homes original one, and the new one requires less amps than the original, if that is the only disconnect for the AC then it is “over fused” however it may have an outside disconnect rated lower.



It does have a pull fuse at the unit outside.

What is that rated at??



30amps. Buy isn’t that for when the unit is being serviced? That way the power can be disconnected at the unit. It doesn’t trip?

Gary, it’s still a fuse isn’t it??? that will blow at 30 amps, well before the breaker would trip wouldn’t it??

Do you have a picture of the data plate you can post?


What about the first pic with the oxidation? Is this an issue that should be called out? Could that connection become a problem in the furture?

The wire being used for the AC is 12/2 awg. It is stamp on the outside of the wire. Wouldn’t this wire be under sized for the breaker,40amp, even though the min. amps is 23.6 on the boiler plate?

When dealing with any motor load the breaker or fuse MUST be able to let the motor start.
The fuse or breaker is installed for the SOLE purpose of opening in the event that the hot wires get shorted to each other or to some part of the metal that encloses them.

The AC unit will have an integral overload device that is responsive to motor current. This integral over load will open in the event that the unit starts overheating and also protects the conductors that are installed to the unit.

So Mike, The wire being smaller than the breaker, which is 40 amps double pole, is ok, since the amps on the boiler plate,ac, is 23.6amps?

Gary, as others have said you really need the manufacturers installation instructions. A 12awg is rated for 25amps when starting a motor (a compressor is a motor) If the Full load amp figure is 23.6amps for that compressor it should normaly run at about 75% of that or about 18 amps, the breaker size should also be that recommended by the manufacturer (the 30 amp outside disconnect MAY be correct).

The reason I am saying I doubt that the conductors are a 12/2 is that both the wires feature black insulation, I have never seen a 12/2 where both conductors are black. That is not to say that the wires are not 12awg, I just don’t think that that is a 12/2 cable assembly.

Do you have either a picture of the data plate or the model number, the former should list the conductor and OCPD ratings, or if you have the model # you should be able to find a copy of the installation instructions on the web.



They colored the white wire black.

Ah, OK that I couldn’t see. Normally they just put a piece of tape on it to indicate an ungrounded conductor.



This is correct. The AC unit will pull around 18.88 amps running but will need to pull around 100 amps in order to start. The trip curve of a 40 amp breaker will allow the AC unit to start and the integral over load will protect the unit and conductors from overload in the event something were to go wrong with the compressor.

I want to be clear on this. 100amps on startup is ok for 12/2 awg.

Without providing a label or a model number an definitive answer cannot be given.

100 Amp on start is not the issue. The trip curve of the protection device and the length of time the current is actually at that level are.


where the heck did the 100amps come from?


Post #16 by Mike Whitt.

Though I would think the LRA would be more accurate a number.